We propose to study the degeneration and regeneration of uniquely identifiable neurons in three invertebrate species using electrophysiological, ultrastructural, and biochemical techniques. In particular, we will examine trophic interactions between nerves, muscles and glia which might account for the 150-250 day survival time of severed motor and CNS axons in crayfish. We shall also examine physiological and ultrastructural correlates of degenerating and regenerating nerve terminals with particular attention given to the status of their synaptic vesicles. We also propose to study the regeneration of CNS ganglia in earthworms and leeches in order to study some rules for axonal connection and ganglionic development that may well be applicable to developing or regenerating neurons in other organisms. For example, results obtained from regenerating earthworm ganglia should provide data on the specificity of axonal reconnection at the level of single identifiable neurons and allow us to distinguish between several possible mechanisms postulated to guide axonal outgrowth.